(1) Field of the Invention
The present invention relates to a plated article of a transparent acrylonitrile-butadiene-styrene resin (hereinafter referred to as "ABS resin") obtained by wet plating. Herein, the term of "transparent" is used as merely meaning a light-transmitting property, not transparent like glass.
(2) Description of the Prior Art
The ABS resin is known as a resin suitable for a plastic plating (e.g. "A Study of the Etching Effect on the Metal-to-ABS Surface Adhesion in Electroless Plating", S. P. Poa, C. C. Wan & C. J. Wu, Metal Finishing, Aug. 13.about.16 (1977); "A study of Factors Affecting Peel Adhesion of Electroplated Coatings on ABS and Polypropylene", J. K. Dennis and P. Tipping, Electroplating and Metal Finishing, Nov. 9.about..noteq.(1974); Japanese Pat. Kokai Koho No. 54-103456).
A plated resin article obtained by plating of a transparent ABS resin, especially a partially plated resin article, has an information display function utilizing as a signal a change of the intensity of transmitted light and/or the color of transmitted light, because an unplated portion (non-plated portion) has a light-transmitting property. For example, the shape of the non-plated portion is utilized as a symbol indicating a function state to be discriminated by this symbol. As specific embodiments, there can be mentioned applications to switches and push buttons of light electric appliances, and if a shape of a letter is given to the non-plated portion, the on-off state of a switch or push button indicated by this shape can be displayed.
Although a plated resin article obtained by plating of a transparent ABS resin is industrially valuable, only a very few products of this type are practically utilized. This is because it is difficult to form a tight wet-plating layer on a transparent ABS resin.
In a plated resin article, since the difference of the linear thermal expansion coefficient between the metal phase and the resin phase is very great, peeling of the plating layer from the surface of the resin is readily caused according to the change of the ambient temperature, and this undesirable phenomenon is especially conspicuous in a transparent ABS resin.
In the production of a transparent ABS resin, it is generally necessary to accord the refractive index of the dispersed rubber phase with that of the continuous resin phase, and for this purpose, methyl methacrylate is ordinarily added to monomers constituting the continuous resin phase. However, we have found that where a compound having an ester bond is contained in the continuous resin phase, the adhesion of the plating layer in the final plated ABS resin article is extremely poor. In view of this fact, in order to obtain a plated article of a transparent ABS resin having a plating layer excellent in the adhesion, it is considered necessary to subject a transparent ABS resin, which does not contain a compound having an ester bond, that is, methyl methacrylate, in the continuous resin phase, to wet plating.